Electrode structure for electron tubes



March 28, 1961 H. D. DOOLITTLE ELECTRODE STRUCTURE FOR ELECTRON TUBES Filed Dec. 4, 1958 INVENTOR.

HOWARD D. DOOLITTLE AGENT United States ELECTRODE STRUCTURE FOR ELECTRON TUBES Filed Dec. 4, 1958, Ser. No. 778,148 7 Claims. (Cl- 313-69) This invention relates to improvements in electrode structures of multi-electrode power tubes and has particular reference to indirectly heated oxide-coated cylindrical cathodes and cooperating control grid structures for use in beam-forming electron tubes.

The present invention embodies novel anode, cathode and control grid structures wherein the effective elements of the control grid are positioned out of the electron flow paths and, therefore, subject to little electron bombardment and consequent grid current, and are also positioned in exceptionally closely-spaced relation to the cathode, thereby requiring lower than normal grid driving power.

One serious problem in the manufacture and operation of multi-electrode power tubes is heating of control grid wires when bombarded by electrons emitted by the cathode. A second problem is the relatively high driving power which must be applied to a control grid to properly influence the flow of electrons between cathode and anode. Grid driving power can be reduced by moving the grid closer to the cathode, when this is possible.

In accordance with the present invention the cathode surface is provided with spaced emitting areas, and the surfaces between the emitting areas are recessed. Grid Wires extend parallel with respective recessed surfaces and are located partially within the recesses. Since portions of the grid wires actually lie interiorly of the cathode with respect to the configuration defined by a line drawn through and connecting the outermost surfaces of the cathode, grid driving power is considerably reduced. This particular structure also considerably reduces bombardment of the grid wires by electrons emitted by the emissive areas of the cathode, thus reducing grid current.

It is, accordingly, a primary object of this invention to provide a novel cathode and cooperating grid and anode structures in a multi-electrode power tube which reduce grid current and grid driving power.

Another object is the provision of a cathode of novel shape embodying convolutions whereby control grid wires may be placed in spaced non-conducting relation to the cathode but still within the cylinder defined by the outer portions of the cathode surface.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, wherein- Fig. l is a front elevational view of a sectioned anode, a cylindrical cathode and a fragmentary control grid embodying the novel structures of this invention;

Fig. 2 is a horizontal sectional view taken on line 2-2 of Fig. 1; and

Fig. 3 is an enlarged fragmentary horizontal sectional view of a portion of the electrode structures.

Referring to the drawings, the cathode preferably comprises a tube or cylinder of metal which is provided on its outer surface with parallel longitudinally-spaced electron emissive areas 11. The emissive areas 11 preferably are relatively thin coatings or strips of a selected material known to have the ability when heated to emit atent O Patented Mar. 28, 1961 profuse quantities of electrons, and the strips 11 may extend the entire length of the cathode cylinder or may terminate short of the ends thereof as shown.

The preferred cathode structure embodies longitudinally extending grooves 12 within the lower portions of which lie the strips 11 (see Fig. 3). When a selected electrical potential is applied between the anode 17 and cathode cylinder 10, and to the control grid wires 16, the uncoated portions of the grooves 12 function to focus the electrons emitted by strips 11 into beams directed toward the anode 17. Heating of the cathode is accomplished by means such as a heater 13 (Fig. 2) within the cylinder 10.

The areas 14 which lie between the grooves 12, which areas are referred to herein as lands, are also provided with respective longitudinally extending grooves 15/ opposite which are located respective parallel grid elements or wires 16. In accordance with this invention the grid wires 16, when expanded by heat during operation of the tube, actually lie partially within the respective grooves 15, and such close proximity with the cathode enables the grid to be driven at a lower rating.

Also, since there are raised portions of the cathode between each pair of grooves 12 and 15, these raised portions tend to partially shield the grid wires from the emissive strips 11, thus reducing electron bombardment and consequent grid heating. 7

Fig. 3 clearly illustrates the location of the expanded grid wires within the cathode structure. The high points of the cathode define a circular configuration depicted by are A-A, and it will be noted that a portion of each grid wire 16 lies interiorly oft-he cathode with respect to are A-A. The wires 16 must, however, be maintained out of actual contact with the cathode so that different electrical potentials. may be applied to the respective electrodes.

It is to be understood that although the cathode is shown in the drawings as being of cylindrical shape, it may be made flat if desired, in which case the raised surfaces will lie substantially in a plane which would be indicated in Fig. 3 by a straight line instead of the arc A-A. Also, grooves 12 need not be arcuate in crosssection as shown but may be flat-bottomed or irregularly shaped if desired.

Other changes may be made by those skilled in the art without departing from the spirit of the invention.

I claim:

1. An electrode structure for electron tubes, comprising a cathode, a control electrode and an anode, said cathode having a plurality of parallel spaced electron-emissive areas, the surfaces of the cathode between the electronernissive areas being provided with grooves extending parallel to said areas, and the control electrode embodying elements located opposite respective grooves and extending parallel therewith, said elements when expanded lying partially within the grooves and spacedtherefrom.

2. An electrode structure for electron tubes, said structure comprising a cathode, a control electrode and an anode, said cathode having a plurality of spaced parallel electron-emissive areas separated by nonemissive surfaces, the non-emissive surfaces each being provided with a groove extending parallel with the electron-emissive areas, and the portions of said nonemissive surfaces between the grooves and the emissive areas being raised to provide ridges extending parallel to and between the grooves and emissive areas, and the control electrode embodying elements locatedopposite respective grooves and extending parallel therewith, said elements when expanded lying partially within the grooves and spaced therefrom, and said ridges being of a height sufiicient to isolate the portions of the elements which lie within the grooves from the emissive areas.

3. An electrode structure for electron tubes, said structure comprising a cathode, a control electrode and an anode, said cathode having a plurality of spaced parallel grooves, alternate grooves' being electronemissive and the remaining grooves being non-emissive, and a control electrode embodying elements located opposite respective non-emissive grooves and extending parallel therewith, said elements when expanded having portions lying within said non-emissive grooves and spaced therefrom, the surfaces of the cathode between the grooves being raised above the bottoms of the grooves an amount sufficient to prevent bombardment of the portions of the elements which lie within the non-emissive grooves by electrons from the emissive grooves.

4. An electrode structure substantially as set forth in claim 3 wherein the emissive grooves of the cathode con tain deposits of electron-emissive material.

5. An electrode structure substantially as set forth in claim 3 wherein the cathode is cylindrical.

6. An electrode structure for electron tubes, said structure comprising a hollow cylindrical cathode and an encircling control electrode and an anode, the outer surface of the cathode being provided with spaced longitudinally extending grooves with the outermost ends of the raised surfaces between grooves defining a cylinder, deposits of electron-emissive material disposed within alternate grooves, the remaining grooves being nonemissive, and a heater element within the cylinder of the cathode for heating the cathode and causing electron emission from said deposits, the control electrode embodying elongate elements located opposite respective non-emissive grooves, said elements when expanded having portions lying inwardly of said non-emissive grooves within the cylinder defined by the outermost ends of the raised surfaces between the grooves.

7. An electrode structure for electron tubes comprising a cathode, an anode and a control electrode between the cathode and anode, the cathode being provided on its surface nearest the anode with a plurality of spaced recessed electron-emissive areas separated by nonemissive areas, the non-emissive areas having grooves therein, the raised portions between said recesses and grooves defining a predetermined configuration which may be depicted by a line connecting said raised portions, said control electrode embodying elongated elements located opposite respective non-emissive grooves and in close proximity to said line connecting the raised por tions, the elements being freely expandable into said grooves when heated without making physical shorting contact with the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,054,252 Hausser Sept. 15, 1936 2,130,280 Knoll Sept. 13, 1938 2,459,792 Chevigny Jan. 25, 1949 2,512,858 Hegbar June 27, 1950 2,727,177 Bailey et a1. Dec. 13, 1955 

